Skip to main content

Full text of "Seasoning California black oak"

See other formats


Historic, archived document 

Do not assume content reflects current 
scientific knowledge, policies, or practices. 




By Harvey H . Smith 



* MAINTAINED AT BERKELEY, CALIFORNIA, IN COOPERATION WITH THE UNIVERSITY OF CALIFORNIA . 



Introduction _ 

235632 

The .forest industry of the Pacific Coast is based on the utiliza- 
tion of softwood species, and little attention has been paid to the several 
native hardwoods. S.ome of these hardwood species appear to be suitable for 
general commercial use. One of the most promising is California black oak 
(Querelas kelloggii), which grows extensively in Oregon and California, and 
is particularly abundant on the west slopes of the northern Sierra in can- 
yons within the ponderosa pine belt at 3,000 to 5,000 feet elevation. 

California black oak has been cut on a limited scale for manufacture 
into lumber and flooring. These few efforts in the past have usually met 
with only limited success because the operators often did not produce the 
quality and size of lumber to meet the needs of the prospective buyers and 
because it was usually poorly manufactured and seasoned. Another reason for 
the slow development of the hardwood industry on the Pac if ic . Coast is the 
scattered occurrence of most of the hardwood species. They are decidedly 
scattered when compared to the softwoods growing in the same general area, 
but look considerably more promising when compared to many of the hardwood 
stands of the east from which the present supply is cut. The western hard- 
woods are more difficult to season— than the several species of softwoods 
with which they are associated, and require special methods of manufacture 
and seasoning. 

The present leek of development of the Pacific hardwoods indicates 
the need for more information about these species. The purpose of this 
study was to develop a practical, effective seasoning procedure for Calif- 
ornia black oak so that its utilization can be put on a more sound basis, 
These drying experiments were carried on in cooperation with the Diamond 
Match Company at Stirling City, California. The tests were conducted in 
two phases, one for air drying and another for kiln drying procedures. 



Test Material 

i 

Black oak logs were cut early in June on a logging area near Butte 
Meadows, located in Butte County in the northern Sierra Nevada region of 
California. The logs represented a wide range of both size and Quality,, 
Some logs of marginal size and quality were selected to determine the yield 
from such material. The total log scale was about 18,000 bd. ft. 5 the num- 
ber of large defective logs and small poorly-formed logs made an accurate 
scale difficult, 



The logs were delivered to the mill pond and sawed without delay on 
a seven-foot head saw into 3/4-inch boards , which were ripped into ?- and 
6-inch wide flooring strips. The strips were from 4 to 16 feet long, aver- 
aging about 8 feet. They were piled in 4-feet by 4-feet by 16-feet package 
units using 9 stickers per course. iM o narrow, dry stickers were available 
and most of the stickers used were green Douglas fir and white fir, 1- by 
4-inch by 4 feet in size. Some cull 3/4 by 3-inch flooring strips were cut 
to 4 feet in length and also used for stickers. Dry 1- by 2-inch stickers 
would have been preferable. 



1/ Torgeson, 0. W. , U. S. Forest Products Laboratory Report 1684, "Kiln- 
drying Schedules for 1-inch Laurel, Madrone, Tanoak, and Chinquapin". 



-1- 



Air-drying Test Procedure 



The package units were moved to the air drying yard where they were 
piled three high on good pile foundations. The piles were spaced 12 to 18 
inches apart. Each pile was covered to protect it from the sun. The sides 
were protected by the adjacent piles, but the ends of the piles were open, 
The piling was relatively open, except for the narrow soace between piles, 
and fast drying could be expected. 

2/ 

Sixteen samples— were prepared and placed in the piles on the yard 
to determine the rate of air drying. These samples were weighed at inter- 
vals during the drying period and the moisture content determined. Weather 
reports were kept by the State Division of Forestry at a station only one- 
half mile from the yard; these reports have been used as a record of the 
drying conditions . 

Air -drying results 

The 3/4 by 3-inch and 3/4 by 6-inch strips dried rapidly (fig. i), 
The average moisture content of the stock had reached 20 percent in one 
month ; The wettest samples had dried to less than 20 percent in only 47 
days,, at which time all the stock could have been kiln dried readily with 
Little danger of drying degrade. 

This fast drying was accomplished with no drying defects, such as 
surface checking, end splitting, and honeycombing. Case-hardening stresses 
can not be classed as a drying defect because they develop during any nor- 
mal drying process. These drying stresses can 'be relieved after both yard 
drying and kiln drying by subjecting the stock to humidity conditions that 
will permit a. regain of moisture. Obviously, this can be done more readily 
ixi the kiln, where drying conditions ca.n be controlled, than on the drying 
yard. 

The small size of the flooring strips (3/4 x 3 in. and 3/4 x 6 in,) 
was an important factor in the fast drying without defects under the severe 
air drying conditions that prevailed. The results of this experiment do 
not permit the broad conclusion that all thicknesses of California black oak 
can be air dried readily without drying defects, but the results do show 
that 3/4-ir.ch strips can be air dried successfully when piled properly on 
the yard, Furthermore, this experience with 3/4-inch stock indicates that 
full one-inch stock can be air dried successfully. 

These results show a drying rate that can be duplicated only during 
the active drying season. Similar material handled in the same way, but 
piled during the wet, cold fail and winter season, would require consider- 
ably longer to dry. The danger from surface checking would also be much 
less during this slow drying season, which may be important in air drying 
thicker stock without defects. 



2/ U. S. Forest Products Laboratory Report 1607, "Use of Kiln Samples in 
Operating a Lumber Dry Kiln". 



-2- 




-a 



s 

•H 

CD 

>» 



-P 

fl 
O 

W 

O 
•H 
-P 



to 
at 

a 

•H 

I 

CO 

>» 
,0 



o \. 
to 

0. <M 
•H O 
>* - 

u o> 
-p 



8-, 
•P 
W 

•H 

fn 
O 
O 
rH 

*5h 



C si 

% 



ID 
feO at 

•H -P 



O 



rH 
CO 



A 

-P 



85 
►H 

o 

•H 
rH 

aS 

o 



(Jo)dN3J. HIV 



oi e s it » « n 



O Q O 
rO CJ — o cn 

C/.)AN3JLN00 3UniSI0IN 



oooooooo 

00N(Oin»rON- 



-3- 



Kiln-drying Test Procedure 

Four kiln runs were made in a small experimental dry kiln - and one 
in a large commercial kiln. Each charge in the small kiln contained 400 
to 500 bd . ft. of 3/4-inch strips. E a ch load was 4 feet wide, 8 feet long 
and 4-l/2 to 5 feet high. At the time of the first experimental kiln run, 
this stock had been on the air drying yard four weeks and had dried to a 
moisture content of 26 percent. By the time of the fourth run it had fur- 
ther dried to 18 percent and at the time of drying in the commercial kiln 
had reached a moisture content of only 10 percent. 

The drying conditions used in the first run in the experimental kiln 
were somewhat conservative (fig. 2). Because the results were encouraging, 
the dry bulb temperature during the next run was maintained at 180 F. This 
temperature is more severe than usually used. In run. No. 4 (fig. 3} the 
initial dry bulb temperature of 140° F. was held until the average moisture 
content of the samples was 15 percent, then the temperature was raised to 
180° F. 

The relative humidity conditions during these experimental/ runs were 
controlled to maintain a rather low equilibrium moisture content— ^ The stock 
had already dried considerably during air drying and a moisture gradient was 
already established. The surface fibers were no longer in tension across 
the grain and there was no further danger from checking. Therefore the rela- 
tive humidity in the kiln was lowered to 20 to 30 percent after only a few 
hours at 50 to 60 percent. These low relative humidity conditions were con- 
ducive to rapid drying and could be used safely since the danger from check- 
ing had passed. 

The strips had air dried to such a low moisture content before being 
dried in the commercial kiln that there was no real kiln drying problem. 
The dry bulb temperature was held at 140° F. with a wet bulb depression of 
40° over one night. The dry bulb temperature was then raised to 180° F. , 
while maintaining a 40° F. wet bulb depression (wet bulb temperatures raised 
from 100° F. to 140° P.). Aft er 24 hours of drying the stock was equalized 
for 16 hours at an 8.0 percent equilibrium moisture content (160° P. dry 
bulb and 140° P. wet bulb). The stock was conditioned for two hours at 
160° F. dry bulb temperature and 152° P. wet bulb temperature to relieve dry- 
ing stresses. The total time in the kiln was only 42 hours and could have 
been reduced by several hours had it been necessary to do so. 

Kiln-drying Results 

The results obtained from the four runs in the small experimental 
kiln and one run in the commercial kiln indicate that air dried California 
black oak can be kiln dried as readily as eastern red oak. 



3/ Torgeson, 0. W. , U. S. Forest Products Laboratory, Report 1671, "Small 
Demountable-type Lumber Dry Kiln for Experimental Drying'*. 

4/ Smith, H. H. , U. S. Forest products Laboratory Report 1651, "Relative 
Humidity and Equilibrium Moisture Content Graphs and Tables for Use in Kiln 
Drying Lumber". 



-4- 



180 



170 



0^ 

Uj 

J 140 
k- 



50 



I 30 



20 



70 



60 



50 



40 



30 



20 























KILN 

_ Cnlifnrnin Rln 


RUN No. I 

rk O n k 


3/4 inch 










— — — 

7-15-48 to 7-18- 


-48 










St 


irling Ci1 


y , Calif o 


' n i o 


















































TEMf 


3 E R ATUR 


E 












Note: 
No de 
the kit 
not re 


fects de 
'n drying, 
lieved. I\ 


1 

ve loped 
Drying 
'0 final c 


during 

stresses 

^ondifionir 


>g. 


L — 






























































^ 


EL ATI VE 


1 1 1 t ft s\ 1 f"\ 1 "V 

H U M i D 1 1 


y i 








































_ M 


OISTURE 


CONTEN 


r 



















k. 

1 

£: 
uj 



O 

k. 











10 20 30 40 50 60 

DRYING TIME (HOURS) 



70 



Figure 2. - Test run of 3/4-inch California black oak flooring 
strips in experimental kiln using moderate drying schedule. 



- 5 - 



190 



180 



£ 170 

u] 
Q: 

^160 
ct 

^150 



140 



130 



KILN RUN No.4 
California Black Oak, 3/4 inch 

7-26-48 to 7-29-48 
St i rling City, California 



TEMPERATURE- 



'S 70 

I 

ti 40 



60 



50 



2 

CO 
<0 



3 



20 



I 



Note: 

No drying defects. Drying 
stresses completely relieved 
by final conditioning. 












10 



20 



30 40 50 

DRYING TIME (HOURS) 



Figure 3,- Test run of 3/4-inch California black oak flooring 
strips in experimental kiln using accelerated drying schedule 
with final conditioning. 



- 6 - 



Figures 2 and 3 show the drying conditions in two of the experimen- 
tal runs. The drying time was 66 and 64 hours, respectively. The drying 
conditions in the second, were more severe and the total drying time of 64 
hours includes a 10-hour conditioning treatment to relieve the drying 
stresses . 

Drying defects occurred in only the second experimental kiln run, 
in which the initial temperature was 180° F. In this run severe honey- 
comb developed in some areas of the stock that had been covered by the 
wide, green stickers used during air drying. Y/ood in these areas had been 
covered during air drying and had not been subject to the same drying con- 
ditions as the wood between the stickers. It had not dried to a sufficient- 
ly low moisture content to withstand, the high kiln temperatures without 
serious defects. 

The development of honeycomb in wet areas of this oak, but not in 
adjacent drier areas, substantiates the theory that wood that has been 
dried below- the fiber saturation point!!/ , and thus contains no free water, 
can be kiln dried at high temperatures without danger from drying defects. 

Conclusions 



The results of these experiments indicate that California black oak, 
cut into thin sizes, can be dried in a relatively short time without drying 
defects 

Three-quarter inch stock can be air dried in only 6 weeks' during the 
ffctive drying season, but may require at least twice that long a time during 
the wet, winter weather. The method of piling will affect the rate of dry- 
ing and the extent of warping during air drying. If it is found that 4/4 
or thicker stock checks when piled for air drying by the method used in this 
experiment, modifications of the piling can be made to slow the rate of dry- 
ing and thus reduce the occurrence of drying defects—/. 

The kiln drying of previously air dried 3/4-inch stock is relatively 
easy and can be accomplished in a modern forced-circulation fan kiln in less 
than 3 days without drying defects. A schedule using 140° P. dry bulb temp- 
erature until the moisture content reaches 15 percent and then a final temp- 
erature of 180° F. can be recommended. The initial relative humidity should 
be about 50 percent, but can be lowered to the desired minimum by the end of 
the second, day. 



5/ Stamm, A. J. . U. S. Forest Products Laboratory Report 859, "The Fiber- 
saturation Point of Wood as Obtained from Electrical Conductivity Measure- 
ments" . 

6/ Espena s , L. D. , U. S . Forest Products Laboratory Report 1657, "Air 
Seasoning of Lumber". 



-7- 



The following kiln schedule is suggested for air dried 3/4 flooring 
strips up to 6 inches in width: 



Moisture Content : 
at v.'hich. change 
is to be made, 

percent - : 


Dry 
Bulb 


vv e t : 
Bulb : 


Relative 
Humidity 


Equilibrium 
Moisture 
Content 




r . 


°V 
r . 


M M 4- 

pc t . : 


pet . 


25 


140 


120 


54 


8.0 






: 1UU 


CO 


A 1 
'i . 1 


15 to Final 


180 


: 130 . 


: 26 


: 3.3 


Equalizing (8 to 12 
hrs. for final MC 

of efo to 8%) 


180 


150 


: 47 


5.7 


Conditioning (2 to 
4 hrs . for final 
MC of 6% to 8$) 


: 180 


: 168 


75 


10.1 



-8-